Flat-walled tubing is used in a variety of applications such as heat exchanger units or the like. Due to the variety of applications and the different requirements of each application, it is necessary, therefore, to cut elongate flat-walled tubular stock into a variety of preselected lengths.
To effect cutting of elongate flat-walled tubular stock, it is known to use cutting devices which include rotating circular cutting blades that typically are moved laterally across the respective upper and lower surfaces of the tubular stock and apply a cut thereto. While the most direct way of effecting a cut is to completely cut through the upper and lower tube walls and sever the tubular stock, the material from which the tubular stock is formed, which typically is a ductile metal such as aluminum, deforms relatively easily during such a cutting procedure. As a result, the cutting blades apply undesirable vertical forces to the tube walls such that the material near the interior surfaces of the walls tends to deflect inwardly so as to cause the undesirable formation of radially inwardly projecting burrs and the like.
To minimize the formation of burrs, it is known to apply the rotating cutting blades to the tube walls such that a groove is cut which extends only partially through the thickness of the tube walls. This reduces the deformation of the burrs within the interior of the tubing. Thereafter, the tube is clamped on opposite sides of the grooved portion by clamping devices and at least one of the clamping devices thereafter is displaced relative to the other to break the tube at the groove. However, while reducing the amount of burrs being formed, the rotating cutting blades still apply undesirable forces to the tube walls and consequently, burrs are nevertheless formed by such a procedure.
In an effort to overcome the localized cutting forces associated with the rotating circular cutting blades, U.S. Pat. No. 5,388,745 discloses a cutting apparatus which incorporates opposed cutting blades each having two straight cutting edges on the bottom edge of a cutting insert which are oriented in opposite directions, one of which cuts in a first direction and the other of which cuts in a second direction opposite the first. Each of the cutting edges defines an acute angle with respect to the upper and lower walls being cut. The straight cutting edges are moved transverse to a longitudinal axis of the tubing to cut completely through the wall thickness to sever the tube. As the straight cutting edge is advanced transversely, the depth of the cut increases and the cut progressively advances radially inwards.
However, each of the aforesaid straight cutting edges has a constant angle along its entire length such that the cutting force applied thereby is evenly distributed throughout the thickness of the tube wall. Thus, substantially equal cutting forces are applied at the beginning of the cut when the wall thickness is greatest and after the cut approaches the interior surface of the tubing when the wall thickness is smallest. In addition, since the cutting edges are only located along the bottom edge of a cutting insert and the upper portion is used for mounting of the cutting insert, the cutting blade must be replaced when the cutting edge becomes dull.
Therefore, it is desirable to provide a stationary circular cutting blade which effects cutting of the tube while minimizing the formation of burrs and other undesirable cutting effects. It is also desirable that the cutting blades be indexable so as to provide a plurality of cutting portions on each cutting blade to reduce the frequency of replacing the cutting blade. It is further desirable that each cutting portion be readily movable from an inactive standby position to an active cutting position to replace a previously active cutting portion adjacent thereto which has become dull. Such movement from an inactive standby position to an active cutting position or vice versa is accomplished by incremental rotation of the cutting blade, which blade otherwise remains stationary during a cutting operation. Still further, it is desirable to provide an indexable cutting blade which varies the distribution of the cutting force over the length of the active contact portion such that the vertical component of the cutting force progressively decreases as the cut approaches the interior surface of the tube.